The present invention relates generally to operations and equipment utilized in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a method and apparatus for generating electrical power downhole.
Power for use in a downhole environment has generally in the past been either stored in a device, such as a battery, and conveyed downhole or it has been transmitted via conductors, such as a wireline, from the space or another remote location. As is well known, batteries have the capability of storing only a finite amount of power therein and have environmental limits, such as temperature, on their use. Additionally, batteries are not readily recharged downhole.
Electrical conductors, such as those in a conventional wireline, provide a practically unlimited amount of power, but require special facilities at the surface for deployment and typically obstruct the production flowpath, thereby preventing the use of safety valves, limiting the flow rate of fluids through the flowpath, etc. while the conductors are in the flowpath. Thus, wireline operations are typically carried out prior to the production phase of a well, or during remedial operations after the well has been placed into production.
What is needed is a method of generating electrical power downhole. The method should not require that power be stored in a device and then convened downhole where it is difficult to recharge. The method should also not require that power be transmitted from a remote location via one or more conductors positioned in a production flowpath of a well. It is accordingly an object of the present invention to provide a method whereby power is generated downhole, and to provide an apparatus for such power generation.
In carrying out the principles of the present intention, in accordance with an embodiment thereof, a downhole power generator is provided in which fluid flow therethrough causes vibration of a member therein. Vibration of the member is used to produce electrical power.
In one aspect of the present invention, the member is elongated and extends into a flow passage formed through a housing. As fluid flows through the flow passage, the member vibrates. The member may be secured to the housing at one end, with the other end facing into the fluid flow. Alternatively, the secured end may face in the direction of the fluid flow. The member may be configured to enhance the amplitude and/or frequency of its vibration.
Vibration of the member may be used to generate electrical power in a variety of manners. A power generating assembly may be attached to the member so that, as the member vibrates, the power generating assembly is displaced therewith. Displacement of the power generating assembly causes electrical power to be generated.
For example, the power generating assembly may include a coil and a magnet, with relative displacement being produced between the coil and the magnet as the member vibrates. The power generating assembly may include a piezoelectric material and a mass, with the mass bearing on the piezoelectric material and inducing strain therein as the member vibrates. The power generating assembly may include a piezoelectric material applied to the member, so that strain is induced in the piezoelectric material as the member flexes when it vibrates. The power generating assembly may include a coil and a magnetostrictive material, with strain being induced in the magnetostrictive material as the member vibrates.
In another aspect of the present invention, the member may have a flow passage formed through it, with the member vibrating when fluid is flowed through its flow passage. The member may be in the form of a nozzle or venturi. A varying pressure differential is created across the member as the fluid flows therethrough, causing the member to vibrate. Again, a variety of methods may be used to produce electrical power from the vibration of the member, including inducing strain in a piezoelectric material, inducing strain in a magnetostrictive material, displacing a coil relative to a magnet, etc.
In a further aspect of the present invention, vibration of the member in response to fluid flow may be regulated downhole. For example, the effect of changes in the fluid flow may be regulated by maintaining a velocity of the fluid flow within predetermined limits. Such velocity maintenance may be accomplished, for example, by varying a flow area in response to chances in the fluid flow rate through the flow passage.
These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings.